Yarn feeding apparatus and braking device including an elastic annular membrane

ABSTRACT

A device for braking a yarn and a yarn feeding apparatus having a stationary storage body for a yarn store with an annular withdrawal surface. The braking device includes a frustoconical flexible braking band which is arranged approximately coaxially relative to the withdrawal surface and to which pressure is applied in the axial direction to press the braking band against the withdrawal surface. A ring-shaped membrane made of an elastomeric or rubber material is joined in a force transmitting manner to the braking band and is supported in an outer ring holder. An end region of the annular membrane is bent back inwardly in a direction towards the withdrawal surface and is joined to the braking band thereat.

FIELD OF THE INVENTION

The present invention relates to a device according to the preamble partof claim 1 and to a yarn feeding apparatus according to claim 16.

BACKGROUND OF THE INVENTION

In a device as known from PCT/EP94/00476 (WO 94/20402) the smalldiameter end region of the membrane is connected to the braking bandsuch that the annular membrane extends outwardly from the large diameteredge of the braking band. When the annular membrane is displaced withits ring holder counter to the withdrawal direction of the yarn itundergoes a bending and pulling load from which the axial force load forthe braking band results by which the braking band is pressed againstthe withdrawal surface. The annular membrane unifies in it the springfunction for holding the braking band against the withdrawal surface andthe function of a transmission body transmitting said axial force loadfrom the ring holder to the braking band. In said arrangement, inpractice, an irregular braking effect may occur for the yarn due to amisalignment between the braking band and the withdrawal surface alongthe essentially line-shaped contact zone between the braking band andthe withdrawal surface. Moreover, the braking band is locally distortedcounter to the withdrawal direction of the yarn in a yarn passage regionwhen responding to the friction force and the repelling force of theyarn, said distortion hindering the achievement of a uniform tensionlevel in the withdrawn yarn.

In other yarn feeding apparatuses (U.S. Pat. No. 5,409,043, U.S. Pat.No. 5,316,051), the axial force load is transmitted to the braking bandby means of a hollow body having the shape of a frustocone into whichthe braking band is glued to the inner side of the hollow body. Saidhollow body is supported at its outer side by means of a springarrangement or an annular membrane which is elastic in the axialdirection of the storage body, however, in the radial direction isrelatively rigid. At the other side the hollow body is stiff in axialdirection and elastic in the radial direction such that the flexiblebraking band is apt to deform locally in the yarn passage region anddespite the axial force load. Said design requires multiple parts. Thehollow body is highly loaded and tends to fatigue. The yarn feedingapparatus also consumes a large amount of space.

In another device known from DE-U-94 06 102, a plastic foam ring isglued to the outer side of the braking band which is held in the largediameter end of a rigid, frustoconical hollow body. A spring assemblyengages at said hollow body which generates the axial force load for thebraking band. Due to the relatively forceful spring assembly, the softplastic foam ring is strongly deformed so that the inherent movabilityof the flexible braking band is restricted. The braking band bears ontoa conical withdrawal surface of the storage body.

It is an object of the invention to create a device of the typedisclosed above, as well as a yarn feeding apparatus in which along thecontact zone between the braking band and the withdrawal surface, auniform braking effect can be generated, and in which a substantiallyconstant tension level can be maintained in the yarn being withdrawn.

This object can be achieved by providing a frusto-conical braking bandoriented generally coaxially with the withdrawal surface defined on thestorage body of a yarn feeding apparatus. An elastic annular membrane isconnected at an outer end region thereof having the large diameter to aholding member, and an inner end region of the membrane having the smalldiameter is bent inwardly in a direction toward the withdrawal surfaceand is connected to the braking band.

The device saves space and consists of only two parts. Due to the bendof the small diameter end region of the annular membrane the brakingband is no longer pulled against the withdrawal surface but is pushedagainst it. The braking band properly centers itself in operation thanksto the bend so that the braking effect along the contact zone remainsuniform. It is imaginable that the braking band under the friction forceand the repelling force of the yarn tends to locally enlarge the coneapex angle in the yarn passage region, i.e. to distort in withdrawaldirection. A strong load exerted from the yarn onto the braking band,e.g. as occurs with a strong acceleration of the yarn or in case of highwithdrawal speed, can result in a sickle-shaped gap between thewithdrawal surface and the braking band in which gap the withdrawalresistance for the yarn may decrease. In such operational phases whereinthe tension in the yarn being withdrawn is already increased, due toacceleration or high withdrawal speed, only a negligible contribution tothe tension increase will be added by the braking device. To thecontrary, in case of a low load exerted by the yarn on the braking band,the cone apex angle of the braking band in the yarn passage region willbe reduced locally and thence the braking effect increases in order toraise the then already low yarn tension. This may help to maintainconstant the yarn tension in the yarn being withdrawn. Due to this thedevice then operates with a self-compensation effect, i.e. the brakingeffect automatically is decreased when the yarn tension rises andautomatically is increased when the yarn tension drops. With given outerdimensions of the ring holder mainly by the cross-sectionalconfiguration of the annular membrane, an optimal large radial extensionof the annular membrane can be used for its deformation. Since theconnecting region is situated at an optimal small diameter the inherentmovability or flexibility of the braking band is disturbed as little aspossible, while the bend backwards and inwards (a bend like a U-turn)improves the self-centering capability of the braking band on thewithdrawal surface.

The proper centering of the braking band and the constant tension levelcan be achieved by providing the membrane with a cross-section which,starting from the outer end region thereof, extends generally toward thebraking band, and then extends to a position generally beyond same, andthen extends inwardly toward the radial position of a small diameteredge of the braking band and finally extends, with its bend, to thebraking band.

The major force load-transmission from the annular membrane to thebraking band takes place within the diameter of the contact zone betweenthe braking band and the withdrawal surface. Due to this, the brakingband, preferably being a very thin flexible metal body, distorts itselfin the yarn passage region in case of stronger yarn load by locallyenlarging the cone apex angle in withdrawal direction. This helpsmaintain a constant yarn tension.

The transmission of the force load onto the braking band via themembrane is carried out very uniformly. The annular membrane is veryflexible at the bent region thereof such that the inherent movability ofthe braking band due to the load from the yarn is hindered as little aspossible. The arcuate bend also aids in the self-centering of thebraking band on the withdrawal surface.

With regard to manufacturing, it is advantageous to leave both edges ofthe braking band free.

The self-centering effect of the braking band is enhanced by providingthe membrane with an essentially S-shaped cross-section.

The wall thickness of the membrane, at least in the area of the smalldiameter end region thereof, decreases gradually so that the inherentmovability or flexibility of the braking band is hindered onlyminimally.

The membrane, at the outer end region thereof, is bent in a directionopposite the bend of the inner end region. This outer bend issignificantly deformed when transmitting the force load onto the brakingband. The deformation motions and forces occurring in this region,however, are remote from the braking band so that they do not interferewith the proper operation of the braking band in its braking function.

The membrane, between the inner and outer bent portions has anarc-shaped interconnecting portion which separates or decouples the bentportions from one another.

In accordance with one embodiment, the decoupling of the inner and outerbent portions is enhanced by at least one further concentric undulation.

The bend of the annular membrane at the inner end region thereof havingthe small diameter may be fixed at the outer side and/or at the innerside of the braking band. Gluing or vulcanising lead to very homogenousand durable connection regions. In case that the bend is secured to theinner side of the braking band then the bend grips or folds around thesmall diameter edge of the braking band. Optionally, the connection ismade directly at the small diameter edge of the braking band.

A cone apex angle of the braking band within a range of about 120°, e.g.between 90° and 140°, allows the device to sensitively respond toaccelerations or decelerations of the yarn. In connection with preciseself-centering effect of the braking band at the withdrawal surface, asubstantially constant tension level in the yarn being withdrawn can beachieved.

The withdrawal surface of the storage body is curved convexly, and anessentially line-shaped contact zone exists between the braking band andthe withdrawal surface, in which contact zone the yarn is braked. Agradually tapering inlet leads to the braking nip which is advantageousfor the yarn which during its withdrawal motion (balloon formation) alsomoves crosswise to its running direction. Moreover downstream of thebraking nip, a gradually diverging outlet region is formed in which theoutgoing yarn is able to move freely.

The interconnecting portion between the bent portions has aconfiguration which conforms to the withdrawal surface of the storagedrum, which results in favorable kinematic relations. Theinterconnecting portion and the outwardly situated bend may fulfill anadditional and desirable function, namely the function of a balloonlimiter by which the yarn running with high withdrawal speed can behindered from leaving the surface of the storage drum by too great adistance.

In a yarn feeding device equipped with the braking device according tothe invention, a substantially constant tension level can be achieved inthe yarn being withdrawn due to a proper self-centering of the brakingband. The braking device consumes only mounting space inside the yarnfeeding apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the subject of the invention will be described with thehelp of the drawings, in which:

FIG. 1 is a fragmentary longitudinal cross-sectional view of a yarnfeeding apparatus including a device for braking a yarn, and

FIGS. 2A-2D are fragmentary, cross-sectional views of variations of theannular membrane.

DETAILED DESCRIPTION

A yarn feeding apparatus F, equipped with a device B for braking a yarnY, particularly a yarn feeding apparatus for projectile or gripperweaving machines, includes a schematically indicated housing 1 receivinga drive motor 2 for a winding element 3 as well as a stationary storagebody S. A housing bracket 8 is provided on housing 1. The yarn Y iswithdrawn from a storage bobbin (not shown), is inserted into thehousing 1 from the left side in FIG. 1 and is passed through the windingelement 3 which due to the rotational motion of the drive motor 2 windsthe yarn Y in windings tangentially onto the surface 5 of the storagebody S (yarn store 4). Not shown means impart an advance motion to theyarn windings in FIG. 1 to the right side. At the free front end ofstorage body S a convexly curved withdrawal surface 6 is situated whichis concentric to the axis of storage body S. Coaxial to storage body S ayarn guiding element 7 is provided through which the yarn is withdrawnaxially, such that the yarn Y first is deflected around the withdrawalsurface 6, is pulled through device B simultaneously and is orbitinglike one hand of a clock around said withdrawal surface 6.

A ring holder 11 is secured to a swivel pivot 9 which can be adjusted ordisplaced within housing bracket 8 essentially parallel to the axis ofstorage body S by means of an adjustment device 10. Ring holder 11supports a carrier ring 12. Carrier ring 12 in turn supports an annularmembrane or ring membrane R, e.g. of elastomeric or rubber-likematerial, which membrane is formed essentially S-like in itscross-section. The small diameter inner region of annular membrane R isconnected to a frustoconical braking band T which preferably consists ofthin sheet metal 19 and which is very flexible but stretch-proof.

The annular membrane R includes an outer holding ring flange 13 which isconnected with carrier ring 12. A bend 14 situated radially outwardly ofwithdrawal surface 6, is connected to said outer holding ring flange 13.The bend 14 is connected to a further bend 17 by means of a connectingsection 15 which is--in cross-section--curved arcuately to the outerside. The connecting section 15 is designed like a 180°-arc and has anend part 18 which is secured to the braking band T by gluing orvulcanisation. In the shown embodiment, the inner and outer edges 20, 21of braking band T are free. Within connecting section 15 at least afurther undulation W could be formed. The braking band T defines abraking surface 22 which is continuous in the circumferential directionand wear and heat-proof. Said braking surface 22 bears on withdrawalsurface 6 along a circular contact zone 23. The edges 20 and 21 of thebraking band T, being straight in its cross-section, are spaced fromwithdrawal surface 6. The major part of the connecting section or areawhere the end part 18 adjacent bend 17 attaches to the braking band T issituated inside or radially inwardly of the diameter of contact zone 23.

Depending on the yarn quality processed by the yarn feeding apparatus F,the axial position of the ring holder 11 is adjusted such that apredetermined axial contact pressure is achieved for the braking band T.As soon as the yarn Y is withdrawn, it passes between the braking band Tand the withdrawal surface 6, and additionally is orbiting between thebraking band T and the withdrawal surface 6 like one hand of a clock.The braking band T in the yarn passage region is locally deformed. Inthe vicinity of the yarn a sickle-shaped opening may be generated. Theend part 18 and the bend 17 do not interfere with the inherentmovability of the braking band T. In case that the yarn is stronglyaccelerated or is withdrawn at a high speed, the friction force and therepelling force imparted by the yarn onto the brake band T arerelatively high. The braking band T thus is tilting in the passageregion of the yarn slightly, e.g. in the withdrawal direction (increaseof the cone apex angle α), such that the braking effect is decreasing.In case of low yarn speed or in case of decreasing yarn speed the forcesfrom the yarn on the braking band are also decreasing. The brake bandcan distort opposite to the withdrawal direction and in the yarn passageregion such that the cone apex angle α becomes smaller. According tothis the braking effect automatically is increasing. The braking deviceautomatically is adapting in this manner to the respective requirementsin order to maintain a substantially constant tension level in the yarnbeing withdrawn.

According to FIG. 2a, with edge 21 of braking band T left free, theconnecting region between end part 18 of bend 17 and the braking band Tis situated within or radially inwardly of the diameter of the contactzone 23. According to FIG. 2b, the bend 17 with its end part 18 gripsaround edge 21 of braking band T. According to FIG. 2c, the transitionfrom end part 18 into bend 17 is situated at edge 21 of braking band T.According to FIG. 2d, end part 18 of bend 17 covers almost the entireouter surface of braking band T.

Although a particular preferred embodiment of the invention has beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

What is claimed is:
 1. A device for braking a yarn during withdrawalthereof from a yarn supply stored on a storage body, the storage bodydefining an axis and an annular withdrawal surface from which the yarnis withdrawn in an orbiting motion therearound and guided through aguide element oriented generally coaxially relative to the withdrawalsurface, said device comprising:a frusto-conical and flexible annularbraking band oriented generally coaxially relative to the withdrawalsurface and axially biased thereagainst; and an elastic annular membranehaving an outer region supported by a ring-shaped holder, an innerperipheral region having a diameter less than a diameter of said outerperipheral region and defining a bent portion which bends inwardlytoward the withdrawal surface, said bent portion being connected to saidbraking band such that said membrane transmits axial force to saidbraking band.
 2. The device of claim 1 wherein said membrane, whenviewed in cross-section taken radially therethrough and starting at saidouter peripheral region, extends generally radially inwardly toward saidbraking band and then to a location generally axially beyond saidbraking band, and from said location said bent portion extends generallyaxially toward an inner peripheral edge of said braking band and isconnected thereat.
 3. The device of claim 1 wherein said braking band isbiased against the withdrawal surface such that an annular contact zoneis defined therebetween, and a connection area is defined at thejunction of said bent portion and said braking band, a substantialportion of said connection area being disposed radially inwardly of saidcontact zone.
 4. The device of claim 1 wherein a connection area isdefined at the junction of said bent portion and said braking band and atransitional area of said membrane defined between said bent portion andsaid connection area is disposed closely adjacent an inner peripheraledge of said braking band.
 5. The device of claim 1 wherein said bentportion is arc-shaped and defines an arc length of about 180 degrees. 6.The device of claim 1 wherein a connection area is defined at thejunction of said bent portion and said braking band, said braking banddefines an inner peripheral edge and an outer peripheral edge having adiameter greater than said inner peripheral edge, said connection areabeing disposed between said inner and outer peripheral edges such thatsaid peripheral edges of said braking band are free of connection tosaid membrane.
 7. The device of claim 1 wherein said membrane has agenerally S-shaped cross-sectional configuration taken radially throughsaid membrane.
 8. The device of claim 1 wherein a wall thickness of saidmembrane at least adjacent said inner peripheral region decreasesgradually in a direction toward said braking band.
 9. The device ofclaim 1 wherein said bent portion is a first bent portion, and saidouter peripheral region of said membrane is defined by a second bentportion and a flange, said flange being connected to said ring-shapedholder, and said second bent portion has a curvature which is reversedfrom a curvature of said first bent portion.
 10. The device of claim 1wherein an undulation is disposed between said inner and outerperipheral regions and extends circumferentially about said membrane.11. The device of claim 1 wherein said braking band defines a firstsurface which faces the withdrawal surface and a second surface whichfaces away therefrom, said bent portion being connected to one of saidfirst and second sides of said braking band via adhesive orvulcanization.
 12. The device of claim 1 wherein said braking band isoriented in a plane which defines an angle of about 120 degrees with theaxis defined by the storage body, said angle comprising a cone apexangle.
 13. The device of claim 1 wherein said membrane includes anintermediate region disposed between said inner and outer peripheralregions, said intermediate region having a shape which generallyconforms to the shape of the withdrawal surface of the storage body. 14.The device of claim 1 wherein said bent portion is a first bent portionand said membrane includes an intermediate region disposed between saidinner and outer peripheral regions, said membrane, when viewed in radialcross-section and starting at said outer peripheral region thereof,includes a second bent portion which forms at least part of said outerperipheral region and which has a reverse curvature than that of saidfirst bent portion, said second bent portion smoothly adjoining saidintermediate region which is spaced from and has a shape which generallyconforms to a shape of the withdrawal surface, said intermediate regionsmoothly adjoining said first bent portion, and said first bent portioncurving towards said braking band and having a terminal end portionconnected thereto.
 15. The device of claim 14 wherein said outerperipheral region includes a flange which is disposed radially outwardlyof said second bent portion and which is connected to said holder, saidbraking band is biased against the withdrawal surface such that anannular contact zone is defined therebetween, and a connection area isdefined at the junction of said first bent portion and said brakingband, a substantial portion of said connection area being disposedradially inwardly of said contact zone.
 16. A yarn feeding apparatuscomprising:a storage body for storing a yarn supply in windings thereon,said storage body defining an axis and an annular withdrawal surface; aguide element through which yarn is guided during withdrawal thereoffrom said withdrawal surface, said guide element being disposed adjacentsaid withdrawal surface and oriented generally coaxially relativethereto; a braking device positioned adjacent said storage body, saidbraking device including:a frusto-conical and flexible annular brakingband oriented generally coaxially relative to said withdrawal surfaceand axially biased thereagainst such that as yarn is withdrawn axiallyfrom said withdrawal surface the yarn orbits between said braking bandand said withdrawal surface; and an elastic annular membrane having anouter peripheral region supported by a ring-shaped holder, an innerperipheral region having a diameter less than a diameter of said outerperipheral region and defining a bent portion which bends inwardlytoward said withdrawal surface, said bent portion being connected tosaid braking band such that said membrane transmits axial force to saidbraking band.
 17. The yarn feeding apparatus of claim 16 wherein saidwithdrawal surface has a convex curvature.
 18. The yarn feedingapparatus of claim 17 wherein said membrane includes an intermediateregion disposed between said inner and outer peripheral regions, saidintermediate region having a shape which generally conforms to saidconvex curvature of said withdrawal surface.
 19. The yarn feedingapparatus of claim 16 wherein said withdrawal surface is generallyconvex in shape and said membrane positions said braking bandtangentially relative to said withdrawal surface.
 20. The yarn feedingapparatus of claim 19 wherein said bent portion is a first bent portionand said membrane includes an intermediate region disposed between saidinner and outer peripheral regions, said membrane, when viewed in radialcross-section and starting at said outer peripheral region thereof,includes a second bent portion which forms at least part of said outerperipheral region and which has a reverse curvature than that of saidfirst bent portion, said second bent portion smoothly adjoining saidintermediate region which is spaced from and has a shape which generallyconforms to said convex shape of said withdrawal surface, saidintermediate region smoothly adjoining said first bent portion, and saidfirst bent portion curving toward said braking band and having aterminal end portion connected thereto.